1. Field of the Invention
The present invention relates to a ribbed plate for a composite slab.
2. Description of Related Art
In building with composite slabs, different profiled ribbed plates made of steel sheet are being used around the world, the steel sheets differing from each other mainly in their outward appearance. One of the most popular ribbed plates in Europe is a steel ribbed plate provided with dovetail-like ribs. Among the best properties of this plate is its favourable appearance, because its lower surface is relatively smooth, and the possibility of attaching heavy loads in the dovetail grooves of the plate by means of special brackets without making holes in the plate itself.
The weakness of, for example, the dovetail profile is, however, an imperfect adhesion to the concrete cast on the plate. Attempts to improve the adhesion have been made by increasing the pattern, for example, protuberances in the upper flange and web of the rib. The problem has, however, not been solved, but in some cases cost-increasing measures have been necessary, for example, deformation of the rib ends in a so called heading.
Because of the vertical component of the adhesion forces and the different bending stiffnesses of the ribbed plate and the concrete, the ribbed plate and the concrete show a tendency to disengage from each other, i.e. they repel each other, which for its part makes the adhesion between the ribbed plate and the concrete weaker. The weak adhesion and the repulsion reaction lead to brittle breaking behaviour. This has resulted in that reduction coefficients of durability have to be used in dimensioning, and essential limitations in the plasticity theoretical dimensioning.